Liquid Liquid Extraction | Lecture notes Chemical Experimentation

CHEM 212: Organic Chemistry Lab 6 - Liquid-Liquid Extraction

and Separation of Organic Compounds

Adapted from Kylie L. Luska, J. Chem. Educ, 2022, 99, 4124-4133.

Assigned reading: Mohrig 4th Edition, Part 3, Section 10.

Assigned exercise: Why should you look up the density of an organic solvent before using it in

an extraction? What is meant by the term ‘immiscible’ and why is this factor important when

performing an extraction?

____________________________________________________________________________

Background: Extraction is an important and commonly used technique in a lab to separate and

purify organic compounds. Extractions are based on the principle “like dissolves like” meaning

compounds with similar properties to the extraction solvent get extracted into that solvent.

Organic compounds maybe separated from one another by partitioning them between two

solvents (one organic and the other aqueous) depending on their solubility in each. While most

organic compounds are insoluble in water, polar compounds are known to be water soluble. One

can alter the polarity of an organic base or acid by either protonating it or deprotonating it, which

would result in the formation of a charged species which would then be water soluble. In this lab

you will first evaluate the solubility of a selection of dye molecules in an organic solvent and

aqueous solutions of varying pH. You will also be given a sample containing a combination of

an organic acid (carboxylic acid), organic base (amine), and a nonpolar organic compound. Either

the carboxylic acid or amine, as assigned, must be extracted and analyzed by recording the

melting point of the dry solid.

____________________________________________________________________________

Equipment/Materials: Test tubes and test tube rack, Separatory funnel, beakers and Erlenmeyer

flasks as needed, dye solutions in dropper bottles, mixtures of naphthalene or biphenyl with

either benzoic acid or 4-nitroaniline, ethyl acetate, HCl and NaOH solutions, diethyl ether and

petroleum ether.

Safety Precautions: Ethyl acetate, diethyl ether and petroleum ether are volatile and flammable.

Hydrochloric acid is corrosive; Sodium hydroxide is a skin irritant; avoid inhaling and avoid

contact with skin and clothing.

Waste Disposal: The aqueous filtrate should be neutralized and goes down the sink. The organic

filtrate goes in halogenated waste. Leftover solid products go in the solid waste.

______________________________________________________________________________

Procedure:

PART A:

You may pick one each from the following sets of dye solutions provided to you.

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CHEM 212: Organic Chemistry Lab 6 - Liquid-Liquid Extraction

and Separation of Organic Compounds

Adapted from Kylie L. Luska, J. Chem. Educ, 2022, 99, 4124-4133. Assigned reading: Mohrig 4th Edition, Part 3, Section 10. Assigned exercise: Why should you look up the density of an organic solvent before using it in an extraction? What is meant by the term ‘immiscible’ and why is this factor important when performing an extraction? ____________________________________________________________________________ Background: Extraction is an important and commonly used technique in a lab to separate and purify organic compounds. Extractions are based on the principle “like dissolves like” meaning compounds with similar properties to the extraction solvent get extracted into that solvent. Organic compounds maybe separated from one another by partitioning them between two solvents (one organic and the other aqueous) depending on their solubility in each. While most organic compounds are insoluble in water, polar compounds are known to be water soluble. One can alter the polarity of an organic base or acid by either protonating it or deprotonating it, which would result in the formation of a charged species which would then be water soluble. In this lab you will first evaluate the solubility of a selection of dye molecules in an organic solvent and aqueous solutions of varying pH. You will also be given a sample containing a combination of an organic acid (carboxylic acid), organic base (amine), and a nonpolar organic compound. Either the carboxylic acid or amine, as assigned, must be extracted and analyzed by recording the melting point of the dry solid. ____________________________________________________________________________ Equipment/Materials: Test tubes and test tube rack , Separatory funnel, beakers and Erlenmeyer flasks as needed, dye solutions in dropper bottles, mixtures of naphthalene or biphenyl with either benzoic acid or 4-nitroaniline, ethyl acetate, HCl and NaOH solutions, diethyl ether and petroleum ether. Safety Precautions: Ethyl acetate, diethyl ether and petroleum ether are volatile and flammable. Hydrochloric acid is corrosive; Sodium hydroxide is a skin irritant; avoid inhaling and avoid contact with skin and clothing. Waste Disposal: The aqueous filtrate should be neutralized and goes down the sink. The organic filtrate goes in halogenated waste. Leftover solid products go in the solid waste. ______________________________________________________________________________ Procedure: PART A: You may pick one each from the following sets of dye solutions provided to you.

I) Methylene Blue or Direct Red 81 II) Solvent Blue 59 or Sudan Red 7B (aka Solvent Red 19) III) Sudan Orange or Nile Blue A

Exercise for Part A (5 pts.)

Before beginning your experiment, predict whether the three dye molecules you have selected will be more soluble in organic solvent or water at pH 7 by examining the structures of the molecules (provided above). Also predict whether an acid–base reaction will take place when the three dyes are subjected to acidic (pH = 0) or basic (pH = 14) solutions. Make a note of your predictions in your lab notebook and get it initialed by your TA.

PART B:

You will be provided with ~ 500 mg of one of the following four mixtures 4 - Nitroaniline/Naphthalene, 4 - Nitroaniline/Biphenyl, Benzoic acid/Biphenyl or Benzoic acid/Naphthalene. Weigh your sample and then dissolve it in ~ 2 5 mLs of ethyl acetate in a beaker. Pour the ethyl acetate solution into the separatory funnel. Complete the transfer by rinsing with small quantities of ethyl acetate. To the ethyl acetate solution (organic layer), add 10 mL of 1M NaOH. Stopper the separatory funnel, shake and vent several times. Drain the organic and aqueous layers into two different flasks. (Think: Is the aqueous layer the one on the bottom or the top?). Pour the organic layer back into the separatory funnel and repeat the extraction with a fresh 10 mL portion of 1M NaOH. Once again remove both the organic and the aqueous layers. At this point you may combine the aqueous layers in a flask labelled ‘Basic’ keep it aside. Rinse and clean your separatory funnel with plenty of water. Pour the organic layer back into the funnel. Repeat the extraction, this time using 10 mLs of IM HCl. As before extract the organic layer twice with two 10 mL portions of acid and combine and store the aqueous layer as before in a clean flask labelled ‘Acidic’. Place both flasks containing the aqueous layers in an ice-bath. To the ‘Basic’ aqueous layer add ~6 mL of a 3M solution of HCl in drops. Continue adding acid till the solution is strongly acidic as measured by litmus paper. And to the ‘Acidic’ aqueous layer add ~ 6 mL of a 3M solution of NaOH in drops till the solution is strongly basic. Do both additions carefully and report your observations. In particular watch for the appearance of a precipitate in either flask. This will indicate what the identity of the second component was in your mixture, whether it was the organic acid (benzoic acid) or the organic base (4-nitroaniline). A solid precipitate should form and remain in one of the two. Leave the solution in the ice bath for ~ 5 minutes for maximum crystal formation. Vacuum filter and rinse with cold deionized (DI) water. Allow to air dry. Weigh the solid and identify it by performing a complete melting point analysis, including a mixed melting point measurement to positively conform the identity of your unknown

Post Lab Discussion:

Is the 4 - nitroaniline in the aqueous or organic layer? What about the benzoic acid?
Both benzoic acid and 4 - nitroaniline are soluble in ethyl acetate and have limited solubility in water. Yet, one of these components ended up in the aqueous fraction. Discuss why the solubility of this component changed under the conditions used for the extraction.
Based on your melting points, was your extraction successful?
Discuss any “Think” questions above which have not already been addressed.

Name the technique that will be used to identify the unknown once it is isolated. (5 pts.)
Name the glass container that was used to perform the extractions. (5 pts.)
When you performed this experiment in the lab you were provided with one of the following mixtures. Indicate which compound is neutral in each case. (5 pts.) a) 4 - Nitroaniline/Naphthalene b) 4 - Nitroaniline/Biphenyl c) Benzoic acid/Biphenyl d) Benzoic acid/Naphthalene
Assume you are performing an extraction with mixture (c) Benzoic acid/Biphenyl (5 pts.) a) Which of the two compounds (i.e. benzoic acid and biphenyl) will get ionized when it is washed with NaOH? b) After the extraction once the layers have separated, which layer will contain the biphenyl and which layer will contain the benzoic acid?

How much of the unknown mixture was used in the experiment? How much of the acidic or basic compound did you isolate at the end of the lab experiment? What was the % yield of your extraction? ( 10 pts.)
What was the molarity of the NaOH solution that was used for the initial extraction? ( pts.)
Why does the separatory funnel need to be ‘vented’ every once in a while? (5 pts.)
What was the main component of the organic layer? (5 pts.)
Was the organic layer on the top or the bottom of the separatory funnel? Why? (5 pts.)

Liquid Liquid Extraction, Lecture notes of Chemical Experimentation

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CHEM 212: Organic Chemistry Lab 6 - Liquid-Liquid Extraction

and Separation of Organic Compounds

Exercise for Part A (5 pts.)

PART B: